The current development towards truly mobile computing and networking has brought on the evolvement of various access technologies that also provide the users with access to the Internet when they are outside their own home network. At present, wireless Internet access is typically based on either short-range wireless systems or mobile networks, or both.
Short-range wireless systems have a typical range of a few tens of meters to one hundred meters. They often combine with systems wired to the Internet to provide communication over long distances. The category of short-range wireless systems includes wireless personal area networks (PANs) and wireless local area networks (WLANs). They have the common feature of operating in unlicensed portions of the radio spectrum, usually either in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band or in the 5 GHz unlicensed band.
Wireless personal area networks are cost-effective and use low power wireless devices that have a typical range of about ten meters. One of the better-known examples of wireless personal area network technology is Bluetooth, which uses the 2.4 GHz ISM band. It provides a peak air link speed of one Mbps, and power consumption low enough for use in personal, portable electronics such as PDAs and mobile phones. Wireless local area networks generally operate at higher peak speeds of about 2 to 100 Mbps and have a longer range, which requires greater power consumption.
The development referred to above has also brought on the evolvement of so-called ad-hoc networks, which offer unrestricted mobility without any underlying infrastructure. The nodes of an ad-hoc network may be mobile or wireless, with examples of such networks including the mobile ad-hoc network (MANET) and the smart sensor network (SSN). Unlike traditional wireless networks, ad-hoc networks need not necessarily rest on an underlying infrastructure, such as base stations. Instead, all the nodes of an ad-hoc network share the responsibility of network formation and management. In an ad-hoc network, each node therefore acts as a router transmitting data/messages to other nodes of the network, and intermediate ad-hoc nodes relay the data/messages between two nodes located far apart from each. Standalone ad-hoc networks are useful at least whenever it is impossible to use a fixed network infrastructure due to geographical, terrestrial, or time constraints, for example. Local ad-hoc networks can also be integrated into legacy networks, such as wireless networks.